1. Field of the Invention
This invention relates to a jewelling and ornamental material and a process for production thereof, and more specifically, to a jewelling and ornamental material which reproduces the play of colors of natural opal and to a process for production thereof.
2. Description of the Prior Art
Natural opal has a structure in which many amorphous silica spheres are regularly aligned in a three-dimensional array. Light incident upon it makes Bragg reflection in a unique play of colors owing to these amorphous silica spheres and pores formed by these spheres. Hence, opal is valued as a jewelling and ornamental material such as a ring, pendant or part of ornamental plate.
However, natural opal has very low mechanical strength because the many amorphous silica spheres are bonded through point-to-point contact. Thus, it has the defect that upon application of heat, the gas within the pores is expanded to break it or develop many fine cracks within the structure whereby it becomes whitely hazy and the play of colors is impaired.
As a material having an equivalent play of colors to natural opal but improved mechanical strength, there has been proposed a jewelling and ornamental material composed of many amorphous silica spheres three-dimensionally arranged regularly in which a resin binder such as an acrylic resin or a styrene resin is impregnated and cured within the pores formed by the above arrangement.
Since the acrylic resin or styrene resin as a binder has poor weatherability, heat resistance and chemical resistance, it develops a yellowish color with the passage of time to reduce the play of colors of the jewelling and ornamental material and degrade its merchandize value. Another defect of this prior jewelling and ornamental material is that the binder dissolves owing to the application of heat or the adhesion of a solvent such as alcohols and benzene and causes distortion or breakage of the jewelling and ornamental material.